Here is another basic question:

One can buy a set of reamers with exact diameters (say 0.25") but also sets
which are 0.001" over-sized and 0.001" under-sized. I can see the reason for
the 0.001" over - this will give a sliding fit. The under-sized reamer is
supposed to be for a press fit but isn't a hole of 0.25" a press fit for an
identical part anyway? Does this depend on material? To get the press fit
with the undersized hole does one need to do other manoeuvres e.g. heat up
the parts etc.?

Thanks,

--
Michael Koblic,
Campbell River, BC

"Michael Koblic" wrote in message
...
Here is another basic question:

One can buy a set of reamers with exact diameters (say 0.25") but also
sets which are 0.001" over-sized and 0.001" under-sized. I can see the
reason for the 0.001" over - this will give a sliding fit. The under-sized
reamer is supposed to be for a press fit but isn't a hole of 0.25" a press
fit for an identical part anyway? Does this depend on material? To get the
press fit with the undersized hole does one need to do other manoeuvres
e.g. heat up the parts etc.?

Thanks,

--
Michael Koblic,
Campbell River, BC

A press fit actually is an interference fit. You can find the interference
amount for a given diameter in handbooks. If you heat the female part and/or
chill the male part, you have either a shrink fit, or temporary impotence
and a frustrated partner.

--
Ed Huntress

A .250 reamed hole will accept a .250" hardened and ground dowel pin
using a small arbor press or just some serious hand pressure. Apply any
reasonable torque to the resulting assembly and it will spin. The .249"
hole in something like aluminum or stronger will be press fit, can take
as much torque as the shaft will handle. I need to temper the last
statement in that the strength of the materials shows up: something with
a low yield point will never tighten up much.

The assembly can be done with heat although a .250 rod is a lousy
example: it is so small in relation to the surface area that it loses
heat VERY rapidly. A 2.50" hole and shaft is a different story.

We do aluminum shrink fit with the female part at about 400 degrees F
(the max to push 6061-T6 without worrying about ruining the heat treat)
and the other part in liquid nitrogen at -278F. Nets out to about 650
degrees F difference. At 13 x 10^-6 per inch per degree that is about
..008" per inch of diameter. That is plenty for a nice drop in fit. But
you have to work fast, we keep the press ready in case there is a snag.

Michael Koblic wrote:
Here is another basic question:

One can buy a set of reamers with exact diameters (say 0.25") but also sets
which are 0.001" over-sized and 0.001" under-sized. I can see the reason for
the 0.001" over - this will give a sliding fit. The under-sized reamer is
supposed to be for a press fit but isn't a hole of 0.25" a press fit for an
identical part anyway? Does this depend on material? To get the press fit
with the undersized hole does one need to do other manoeuvres e.g. heat up
the parts etc.?

Thanks,

as I recall, from a while back, the swing wing hinge pin on the B2 was
installed per below - nice big pin - 2 or 3 feet diameter titanium, chilled
in LN2 and lowered into place and allowed to warm up, never to move again
"RoyJ" wrote in message
m...
A .250 reamed hole will accept a .250" hardened and ground dowel pin using
a small arbor press or just some serious hand pressure. Apply any
reasonable torque to the resulting assembly and it will spin. The .249"
hole in something like aluminum or stronger will be press fit, can take as
much torque as the shaft will handle. I need to temper the last statement
in that the strength of the materials shows up: something with a low yield
point will never tighten up much.

The assembly can be done with heat although a .250 rod is a lousy example:
it is so small in relation to the surface area that it loses heat VERY
rapidly. A 2.50" hole and shaft is a different story.

We do aluminum shrink fit with the female part at about 400 degrees F (the
max to push 6061-T6 without worrying about ruining the heat treat) and the
other part in liquid nitrogen at -278F. Nets out to about 650 degrees F
difference. At 13 x 10^-6 per inch per degree that is about .008" per inch
of diameter. That is plenty for a nice drop in fit. But you have to work
fast, we keep the press ready in case there is a snag.

Michael Koblic wrote:
Here is another basic question:

One can buy a set of reamers with exact diameters (say 0.25") but also
sets which are 0.001" over-sized and 0.001" under-sized. I can see the
reason for the 0.001" over - this will give a sliding fit. The
under-sized reamer is supposed to be for a press fit but isn't a hole of
0.25" a press fit for an identical part anyway? Does this depend on
material? To get the press fit with the undersized hole does one need to
do other manoeuvres e.g. heat up the parts etc.?

Thanks,

RoyJ writes:

We do aluminum shrink fit with the female part at about 400 degrees F
(the max to push 6061-T6 without worrying about ruining the heat treat)
and the other part in liquid nitrogen at -278F. Nets out to about 650
degrees F difference. At 13 x 10^-6 per inch per degree that is about
.008" per inch of diameter.

I love this newsgroup. Someday I will need to know this.

On Mon, 9 Mar 2009 18:37:46 -0700, "Michael Koblic"
wrote:

Here is another basic question:

One can buy a set of reamers with exact diameters (say 0.25") but also sets
which are 0.001" over-sized and 0.001" under-sized. I can see the reason for
the 0.001" over - this will give a sliding fit. The under-sized reamer is
supposed to be for a press fit but isn't a hole of 0.25" a press fit for an
identical part anyway? Does this depend on material? To get the press fit
with the undersized hole does one need to do other manoeuvres e.g. heat up
the parts etc.?

Thanks,

For interference of .001" I don't employ heat. I just push it in with
a vise or hydraulic press. This probably wouldn't work with long
slender parts, though.

On Mar 10, 2:33*am, Don Foreman wrote:
...
For interference of .001" I don't employ heat. I just push it in with
a vise or hydraulic press. This probably wouldn't work with long
slender parts, though.

For that I ream most of the hole to the size of the pin and leave a
short press-fit section at the far end. I follow the book
recommendations if I have the right reamers, but if not I don't let
the full-sized drill break completely through and use the remaining
tapered rim for the press fit. Another way to adjust the press fit of
an undersized drilled hole is to tap it.

When you don't need a hardened pin it's a lot easier to ream the hole
with the reamer you have and turn the pin to fit. You can lightly
knurl the pin to make it larger, or roll a coarse file over it, use
Loctite, or as a last resort hammer it.

I leave the press-in area relatively rough so compressed ridges have a
place to flow. I cut or file a very slight taper on the end of the pin
and press it a little ways in with the intended pressure, put it back
in the lathe and set the bit to shave a chip (or dust) just past the
end of the press marks. If it won't recenter, file it and use the feel
of a micrometer as a gage.

You can make a drill bit enlarge a slightly undersize hole to size
nearly as well as a reamer by snugging up the quill lock so it doesn't
jump and feeding slowly. Measure the drill bit's diameter right at the
point, the shank may be smaller. With care and a good chuck I can
drill within a thousandth of the measurement. Any runout makes the
hole larger.

Stuff like that is for non-critical home shop jobs on a limited
budget. When you build something and use it yourself, you can get away
with a lot more. You know what's weak, keep an eye on it, and can fix
it. It becomes a grey area on a free repairs for friends. I'm likely
to admit I don't have the right tools rather than do something
questionable that could break and hurt them.

Jim Wilkins

Jim Wilkins wrote:
For that I ream most of the hole to the size of the pin and leave a
short press-fit section at the far end. ... Another way to adjust the press fit of
an undersized drilled hole is to tap it.

When you don't need a hardened pin it's a lot easier to ream the hole
with the reamer you have and turn the pin to fit. You can lightly
knurl the pin to make it larger, or roll a coarse file over it, use
Loctite, or as a last resort hammer it.

I leave the press-in area relatively rough so compressed ridges have a
place to flow. I cut or file a very slight taper on the end of the pin
and press it a little ways in with the intended pressure, put it back
in the lathe and set the bit to shave a chip (or dust) just past the
end of the press marks. If it won't recenter, file it and use the feel
of a micrometer as a gage.

You can make a drill bit enlarge a slightly undersize hole to size
nearly as well as a reamer by snugging up the quill lock so it doesn't
jump and feeding slowly. Measure the drill bit's diameter right at the
point, the shank may be smaller. With care and a good chuck I can
drill within a thousandth of the measurement. Any runout makes the
hole larger.

Stuff like that is for non-critical home shop jobs on a limited
budget. When you build something and use it yourself, you can get away
with a lot more. You know what's weak, keep an eye on it, and can fix
it. It becomes a grey area on a free repairs for friends. I'm likely
to admit I don't have the right tools rather than do something
questionable that could break and hurt them.


Good stuff! I started to snip & found that there was nothing to leave
out. Very appropriate to the HSM'er.
Bob

On Mar 9, 7:37*pm, "Michael Koblic" wrote:
Here is another basic question:

One can buy a set of reamers with exact diameters (say 0.25") but also sets
which are 0.001" over-sized and 0.001" under-sized. I can see the reason for
the 0.001" over - this will give a sliding fit. The under-sized reamer is
supposed to be for a press fit but isn't a hole of 0.25" a press fit for an
identical part anyway? Does this depend on material? To get the press fit
with the undersized hole does one need to do other manoeuvres e.g. heat up
the parts etc.?

Thanks,

--
Michael Koblic,
Campbell River, BC

They DO sell dowel pins with the same tolerances, .001 under and .001
over, so for your example hole you could ream the mating hole exactly .
250" and use a .249" dowel pin, if you ever wanted to take the
assembly apart again. Clamp together, drill and ream the mating
halves .249", separate and ream one half .250". It just depends on
the design and what you want to do with it. Mostly for jig and
fixture folks.

Stan

On Mon, 09 Mar 2009 21:48:54 -0500, RoyJ wrote:
(top posting obsessively fixed)

Michael Koblic wrote:
Here is another basic question:

One can buy a set of reamers with exact diameters (say 0.25") but also
sets which are 0.001" over-sized and 0.001" under-sized. I can see the
reason for the 0.001" over - this will give a sliding fit. The
under-sized reamer is supposed to be for a press fit but isn't a hole
of 0.25" a press fit for an identical part anyway? Does this depend on
material? To get the press fit with the undersized hole does one need
to do other manoeuvres e.g. heat up the parts etc.?

Thanks,

A .250 reamed hole will accept a .250" hardened and ground dowel pin
using a small arbor press or just some serious hand pressure. Apply any
reasonable torque to the resulting assembly and it will spin. The .249"
hole in something like aluminum or stronger will be press fit, can take
as much torque as the shaft will handle. I need to temper the last
statement in that the strength of the materials shows up: something with
a low yield point will never tighten up much.

The assembly can be done with heat although a .250 rod is a lousy
example: it is so small in relation to the surface area that it loses
heat VERY rapidly. A 2.50" hole and shaft is a different story.

We do aluminum shrink fit with the female part at about 400 degrees F
(the max to push 6061-T6 without worrying about ruining the heat treat)
and the other part in liquid nitrogen at -278F. Nets out to about 650
degrees F difference. At 13 x 10^-6 per inch per degree that is about
.008" per inch of diameter. That is plenty for a nice drop in fit. But
you have to work fast, we keep the press ready in case there is a snag.

What sort of diameters do you use?

I know that shrink fits are routinely used on some wrist pins for
automobile engines, with a hot rod, a room-temperature pin and piston,
and a light (or no) press fit.

I've also been told that this is a way to sleeve out a flathead V-8
engine -- you go ahead and bore out the cylinders until you're into the
water jackets or have at least seriously thinned the walls, then you drop
chilled cast iron sleeves into the heated block.

--
http://www.wescottdesign.com

On Mar 10, 12:04*pm, wrote:

They DO sell dowel pins with the same tolerances, .001 under and .001
over, so for your example hole you could ream the mating hole exactly .
250" and use a .249" dowel pin, if you ever wanted to take the
assembly apart again. *Clamp together, drill and ream the mating
halves .249", separate and ream one half .250". *It just depends on
the design and what you want to do with it. *Mostly for jig and
fixture folks.

Stan

The jig and fixture folks have milling machines accurate enough to
make multiple dowel pins all align. They rarely let me use them.

Yuo can still locate with dowel pins if you have simpler machinery but
you need to make adjustments. As Stan noted, drill and ream them one
at a time without moving the table. This can be difficult on a drill
press or mill-drill with limited quill travel unless you cut the
reamers short. A lathe with a faceplate is very good for precisely
locating and boring holes although the process is slow.

If one dowel pin locates a hole and a second locates a slot, then the
distance between the pins isn't critical. Kinematically this is as
good as two dowel pins in holes, maybe better if you have to bang the
pieces together, but it will wear faster.

If some of the pins end up slanted, drill through so you can punch
them out to unlock and separate the parts.

Jim Wilkins

Boy! Lots of good input so far.
Just a note of caution about reaming softer materials for a press fit:
Over time, some softer materials must flow away from the junction, I
think.
We do a fair amount of pressing steel pins into alumimum bubs that
really take a beating all their life. Take a look at tensile strength
tables for various aluminum alloys and you will see vast differences. I
think one would need to proceed pretty cautiously when designing the
proper fits for the proper applications. This is why the over and under
AND special "decimal" reamers are available.

Pete Stanaitis
-------------------------

Michael Koblic wrote:

Here is another basic question:

One can buy a set of reamers with exact diameters (say 0.25") but also sets
which are 0.001" over-sized and 0.001" under-sized. I can see the reason for
the 0.001" over - this will give a sliding fit. The under-sized reamer is
supposed to be for a press fit but isn't a hole of 0.25" a press fit for an
identical part anyway? Does this depend on material? To get the press fit
with the undersized hole does one need to do other manoeuvres e.g. heat up
the parts etc.?

Thanks,

We do prototype work, nothing is ever the same. aluminum parts
typically, up to a couple inches in diameter. Machining is done by
students, surface finish tends to be marginal, you need plenty of
clearance to get things to work right.

Tim Wescott wrote:
On Mon, 09 Mar 2009 21:48:54 -0500, RoyJ wrote:
(top posting obsessively fixed)

Michael Koblic wrote:
Here is another basic question:

One can buy a set of reamers with exact diameters (say 0.25") but also
sets which are 0.001" over-sized and 0.001" under-sized. I can see the
reason for the 0.001" over - this will give a sliding fit. The
under-sized reamer is supposed to be for a press fit but isn't a hole
of 0.25" a press fit for an identical part anyway? Does this depend on
material? To get the press fit with the undersized hole does one need
to do other manoeuvres e.g. heat up the parts etc.?

Thanks,

A .250 reamed hole will accept a .250" hardened and ground dowel pin
using a small arbor press or just some serious hand pressure. Apply any
reasonable torque to the resulting assembly and it will spin. The .249"
hole in something like aluminum or stronger will be press fit, can take
as much torque as the shaft will handle. I need to temper the last
statement in that the strength of the materials shows up: something with
a low yield point will never tighten up much.

The assembly can be done with heat although a .250 rod is a lousy
example: it is so small in relation to the surface area that it loses
heat VERY rapidly. A 2.50" hole and shaft is a different story.

We do aluminum shrink fit with the female part at about 400 degrees F
(the max to push 6061-T6 without worrying about ruining the heat treat)
and the other part in liquid nitrogen at -278F. Nets out to about 650
degrees F difference. At 13 x 10^-6 per inch per degree that is about
.008" per inch of diameter. That is plenty for a nice drop in fit. But
you have to work fast, we keep the press ready in case there is a snag.

What sort of diameters do you use?

I know that shrink fits are routinely used on some wrist pins for
automobile engines, with a hot rod, a room-temperature pin and piston,
and a light (or no) press fit.

I've also been told that this is a way to sleeve out a flathead V-8
engine -- you go ahead and bore out the cylinders until you're into the
water jackets or have at least seriously thinned the walls, then you drop
chilled cast iron sleeves into the heated block.

On 2009-03-10, Michael Koblic wrote:
Here is another basic question:

One can buy a set of reamers with exact diameters (say 0.25") but also sets
which are 0.001" over-sized and 0.001" under-sized. I can see the reason for
the 0.001" over - this will give a sliding fit. The under-sized reamer is
supposed to be for a press fit but isn't a hole of 0.25" a press fit for an
identical part anyway? Does this depend on material? To get the press fit
with the undersized hole does one need to do other manoeuvres e.g. heat up
the parts etc.?

First off -- the dowel pin may well be a few tenths undersized
for free sliding in a precise hole.

Second -- depending on how firm a grip you need, you may want
more interference. A precise sized dowel pin in a precise sized reamed
hole may well be just a thumb strength press fit. Not counting what
may happen with temperature changes if the hole and the pin are
different materials. What fits at one temperature may be a sliding fit
at another, and something requiring a hydraulic press to install at yet
another. :-)

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

In article , Ed Huntress
wrote:

"Michael Koblic" wrote in message
...
Here is another basic question:

One can buy a set of reamers with exact diameters (say 0.25") but also
sets which are 0.001" over-sized and 0.001" under-sized. I can see the
reason for the 0.001" over - this will give a sliding fit. The under-sized
reamer is supposed to be for a press fit but isn't a hole of 0.25" a press
fit for an identical part anyway? Does this depend on material? To get the
press fit with the undersized hole does one need to do other manoeuvres
e.g. heat up the parts etc.?

Thanks,

--
Michael Koblic,
Campbell River, BC

A press fit actually is an interference fit. You can find the interference
amount for a given diameter in handbooks. If you heat the female part and/or
chill the male part, you have either a shrink fit, or temporary impotence
and a frustrated partner.

I think you can call that an interference fit, too.

-Frank

--
Here's some of my work:
http://www.franksknives.com/

"Frank Warner" wrote in message
. ..
In article , Ed Huntress
wrote:

"Michael Koblic" wrote in message
...
Here is another basic question:

One can buy a set of reamers with exact diameters (say 0.25") but also
sets which are 0.001" over-sized and 0.001" under-sized. I can see the
reason for the 0.001" over - this will give a sliding fit. The
under-sized
reamer is supposed to be for a press fit but isn't a hole of 0.25" a
press
fit for an identical part anyway? Does this depend on material? To get
the
press fit with the undersized hole does one need to do other manoeuvres
e.g. heat up the parts etc.?

Thanks,

--
Michael Koblic,
Campbell River, BC

A press fit actually is an interference fit. You can find the
interference
amount for a given diameter in handbooks. If you heat the female part
and/or
chill the male part, you have either a shrink fit, or temporary impotence
and a frustrated partner.

I think you can call that an interference fit, too.

-Frank

Well, the terms have been established for over 100 years and they're pretty
universal in manufacturing. An interference fit is a press fit in which the
male part is dimensionally larger (by a very small amount) than the female
part. It's done at room temperature. A part that's fitted for interference
by heating of the female and/or chilling of the male is called a shrink fit.
A slip fit is one in which the male is dimensionally smaller than the female
part, also by a very small amount. These don't often slip in place,
actually. They usually require a little pressing.

Of course, a running fit is a looser fit.

--
Ed Huntress